1. Technical Field
This disclosure relates to a liquid ejection head and an image forming apparatus.
2. Description of the Related Art
As image forming apparatuses such as printers, facsimile machines, copiers, plotters, and multi-task machines having plural such functions, ink jet recording apparatuses of a liquid ejection recording type using a recording head that ejects, for example, ink liquid droplets are known. The image forming apparatus of this type ejects ink droplets onto a sheet during conveyance from the recording head to perform image formation (used synonymously with recording, printing, and imaging). Examples of the image forming apparatus include a serial-type image forming apparatus in which the recording head ejects liquid droplets to form an image while moving in a main scanning direction and a line-type image forming apparatus using a line-type head in which the recording head ejects liquid droplets to form an image without moving.
Note that in the present invention, the “image forming apparatus” refers to an apparatus that shoots ink droplets onto a medium such as paper, a thread, a fiber, a fabric, leather, metal, a plastic, glass, wood, and a ceramic so as to perform the image formation. Furthermore, the “image formation” refers to forming on the medium not only relevant images such as characters and graphics, but also irrelevant images such as random patterns (i.e., liquid droplets are just ejected and shot out). Furthermore, the “ink” is not limited to one as generally called ink, but it is used as a generic name of various liquid available for the image formation such as recording liquid, fixing treatment liquid, and liquid. Furthermore, the material of the “sheet” is not limited to paper. That is, the sheet refers to ones including an OHP sheet, a fabric, etc., onto which ink droplets are ejected, and it is used as a generic name of one including a medium to be recorded, a recording medium, a recording sheet, a recording paper, etc.
As liquid ejection heads, piezoelectric-type liquid ejection heads using a piezoelectric-type actuator are known. In this liquid ejection head, plural liquid chambers are independently provided for each of the nozzles arranged in parallel that eject ink droplets, and at least a part of wall surfaces of the plural liquid chambers is formed by a vibration plate. When ejecting ink droplets, the liquid ejection head deforms the vibration plate with piezoelectric elements and changes the volumes of the liquid chambers.
As described in Patent Document 1, such a piezoelectric-type liquid ejection head uses, for example, lamination-type piezoelectric elements. The liquid ejection head includes a flow path member having plural liquid chambers respectively in communication with plural nozzles that eject liquid droplets and are arranged side by side; a vibration member that forms at least a part of the wall surfaces of the liquid chambers; plural piezoelectric element columns composed of lamination-type piezoelectric elements that deform each of the vibration plates corresponding to the liquid chambers; and a base member on which plural piezoelectric elements are arranged.    Patent Document 1: JP-A-2007-069545
In addition, as described in Patent Document 1, it is known that such a liquid ejection head has a bi-pitch structure in which piezoelectric element columns and supporting columns are alternately arranged between the base member and the flow path member at a nozzle arrangement interval. Alternatively, it is known that such a liquid ejection head has a normal-pitch structure in which the piezoelectric element columns are arranged between the base member and the flow path member at the nozzle arrangement interval.
Note that as for the piezoelectric-type liquid ejection head, the following Patent Documents are also known.    Patent Document 2: JP-A-2001-270116    Patent Document 3: JP-A-2004-160941    Patent Document 4: JP-A-2005-034997    Patent Document 5: JP-B2-3454833
Due to the alternate arrangement of the piezoelectric element columns and the supporting columns driven, it is difficult to realize high density in the liquid ejection head having the bi-pitch structure. That is, because the piezoelectric element columns and the supporting columns are arranged relative to a desired nozzle arrangement interval (nozzle pitch), the widths of the piezoelectric element columns and the supporting columns in a nozzle arrangement direction become narrow. As a result, the piezoelectric element columns and the supporting columns are easily damaged during processing, and their bonding strength with the base member is easily reduced.
On the other hand, because the supporting columns are not arranged between the piezoelectric element columns in the liquid ejection head having the normal-pitch structure, the nozzle pitch and the arrangement interval of the piezoelectric element columns can be made the same, which makes it possible to arrange the nozzles at high density. However, due to the absence of the supporting columns between the piezoelectric elements, the liquid ejection head having the normal-pitch structure is likely to cause mutual interference compared with the liquid ejection head having the bi-pitch structure. Specifically, when the liquid ejection head ejects liquid droplets, the piezoelectric element columns expand to thereby upthrust the whole flow path member. As a result, liquid droplet ejection performance from the nozzles is degraded, and meniscus of the nozzles that do not eject liquid droplets is broken. Particularly, when liquid droplets are ejected from a large number of nozzles, the mutual interference becomes pronounced. As a result, the liquid droplet ejection performance is fluctuated.
According to Patent Documents 3 and 4, in order to prevent the mutual interference, the positions of penetrated parts (parts connected to the nozzles of the liquid chambers) of the adjacent liquid chambers are displaced so as to prevent the reduction in rigidity of the parts. Such a method is effective only for the mutual interference between the adjacent liquid chambers (called “adjacent mutual interference”), but it is not effective for the mutual interference caused by upthrusting the flow path member.